1. Field of the Invention
The present invention relates to a substrate processing apparatus, and more particularly to a substrate processing apparatus for removing surface roughness produced at a peripheral portion (a bevel portion and an edge portion) or the like of a substrate such as a semiconductor wafer, or for removing a film attached to a peripheral portion or the like of a substrate which would cause contamination.
2. Description of the Related Art
In recent years, according to finer structures of semiconductor elements and higher integration of semiconductor devices, it has become more important to manage particles. One of the major problems in managing particles is dust caused by surface roughness produced at a bevel portion and an edge portion of a semiconductor wafer (substrate) in a manufacturing process of semiconductor devices. In this case, a bevel portion means a portion having a curvature in a cross-section of an edge of a semiconductor wafer. Further, an edge portion means a flat portion extending about several millimeters radially inwardly from a bevel portion of a wafer.
For example, the aforementioned surface roughness caused by processing is produced in a RIE (Reactive Ion Etching) process of forming trenches (deep trenches) for a trench capacitor on a surface of a Si wafer. In a RIE process, as shown in FIG. 1A, a hard mask comprising laminated films composed of a SiN film 500 and a SiO2 film 510 is first formed on a Si wafer 100, and then the Si wafer 100 is etched by an RIE method while the hard mask serves as a mask, thereby forming deep trenches 520 (see FIG. 1B).
In this RIE process, by-products produced during etching may be attached to a bevel portion and an edge portion of the Si wafer 100 and serve as masks for etching, thereby forming needle projections 530 at the bevel portion and the edge portion of the Si wafer 100, as shown in FIG. 1B. Particularly, in a case of forming, with accuracy, deep trenches 520 having an opening diameter of a submicron and an aspect ratio as high as multiples of ten, the aforementioned needle projections 530 are inevitably produced under such process conditions at the bevel portion and the edge portion.
The heights of the needle projections 530 vary depending on the positions of the needle projections 530 and are as large as about 10 μm at their maximum height. The needle projections 530 are broken in transferring or processing the Si wafer 100 and thus cause particles to be produced. Since such particles lead to a lower yield, it is necessary to remove the needle projections 530 formed at the bevel portion and the edge portion.
A CDE (Chemical Dry Etching) method has heretofore been employed in order to remove such needle projections 530. In a CDE method, a resist 540 is first applied on surfaces except for a region of several millimeters which includes the bevel portion and the edge portion of the Si wafer 100, as shown in FIG. 2A. Then, a portion of the Si wafer 100 that is not covered with the resist 540 is isotropically etched to remove the needle projections 530 at the bevel portion and the edge portion (see FIG. 2B). Thereafter, the resist 540, which has protected the device surfaces, is removed (see FIG. 2C).
With such a CDE method, since device surfaces should be protected by a resist 540, it is necessary to apply a resist and remove the resist. Further, although sharp needle portions can be removed by isotropic etching, irregularities 550 are formed depending on the variation of the heights of the needle projections 530 (see FIG. 2C). These types of irregularities 550 may be problematic because dust tends to accumulate in the irregularities 550 during subsequent processes such as CMP (Chemical Mechanical Polishing). However, the conventional CDE method has difficulty in completely removing such surface roughness at the bevel portion and the edge portion of the Si wafer 100. Further, the time required for processing a single wafer in a CDE process is usually 5 minutes or more, and hence a CDE process has problems in that it causes a lower throughput and has high material costs.
Further, new materials, such as Cu as a wiring material, Ru and Pt as a capacitor electrode material for next-generation DRAM and FeRAM, and TaO and PZT as a capacitor dielectric material, have recently been introduced in the fields of semiconductor devices one after another. Now is the time to seriously consider problems of device contamination caused by these new materials in the mass production of semiconductor devices. Particularly, in a manufacturing process of a semiconductor device, since films of new materials which are attached to a bevel portion, an edge, and a reverse face of a wafer may cause contamination, removal of such films represents an important problem.
For example, when a Ru film to be used as a capacitor electrode is deposited, it is important to remove the Ru film attached to a bevel portion, an edge portion, and a reverse face. Currently, a CVD (Chemical Vapor Deposition) method is generally used as a deposition method of such a Ru film. With the CVD method, attachment of a Ru film to a bevel portion, an edge portion, and a reverse face is unavoidable, while degrees of the attachment are different depending on device arrangements. Even if a Ru film is deposited with an edge cut ring by a sputtering method, it is difficult to completely eliminate the attachment of a Ru film to a bevel portion and an edge portion due to wraparounds of sputter particles (Ru). When an edge cut width is reduced in order to increase a yield of peripheral chips, it is more difficult to completely eliminate attachment of a Ru film.
With any deposition method, a Ru film is attached to a bevel portion, edge portion, or a reverse face of a wafer after Ru deposition. As described above, this type of Ru film attached to a bevel portion or the like should be removed because it causes device contamination in the next processes.
Removal of a Ru film attached to a bevel portion or the like has heretofore been performed by a wet-etching method. A wet-etching method generally includes dropping a chemical liquid onto a Si wafer being rotated horizontally while a reverse face of the Si wafer faces upwardly. With respect to a bevel portion and an edge portion, removal of a Ru film is performed by adjusting a rotational speed or the like to adjust the amount of the chemical liquid flowing onto a device-formed surface.
However, with this method, because a removal rate of a Ru film is about 10 nm/min, a period of time for processing a single wafer is usually as long as 5 minutes or more, thereby resulting in a lowered throughput. Further, it is impossible to remove Ru diffused in an underlying layer, and, in order to remove such Ru, it is necessary to perform additional wet-etching with another chemical liquid that can etch the underlying layer, thereby resulting in a further lowered throughput. Furthermore, this method has another problem in that there are no adequate chemical liquids that do not damage a device.